Orthopedic screw for measuring a parameter of the muscular-skeletal system

ABSTRACT

A dual-mode closed-loop measurement system for capturing a transit time, phase, or frequency of energy waves propagating through a medium is disclosed. A first module comprises an inductor drive circuit, an inductor, a transducer, and a filter. A second module housed in a screw comprises an inductor and a transducer. The screw is bio-compatible and allows an accurate delivery of the circuit into the muscular-skeletal system. The inductor can be attached and interconnected on a flexible substrate that fits into a cavity in the screw. The first and second modules are operatively coupled together. The first module provides energy to power the second module. The second module emits an energy wave into the medium that propagates to the first module. The transit time of energy waves is measured and correlated to the parameter by known relationship.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.12/826,273 filed on 29 Jun. 2010 claiming priority benefit of U.S.provisional patent applications No. 61/221,761, 61/221,767, 61/221,779,61/221,788, 61/221,793, 61/221,801, 61/221,808, 61/221,817, 61/221,867,61/221,874, 61/221,879, 61/221,881, 61/221,886, 61/221,889, 61/221,894,61/221,901, 61/221,909, 61/221,916, 61/221,923, and 61/221,929 all filed30 Jun. 2009; the disclosures of which are hereby incorporated herein byreference in their entirety.

FIELD

The present invention relates generally to measurement of physicalparameters, and more particularly, dual mode real-time measurement ofphysical parameters by evaluating changes in a transit time orpropagating energy waves.

BACKGROUND

Sensors are used to measure or monitor a parameter. Sensors can providequantitative information on the parameter or how the parameter changesover time. For example, a temperature sensor is commonly used to monitorthe operating temperature of a component or a biological entity. Thetemperature sensor can be used to monitor temperatures over a variety ofoperating conditions and formats. Typically, sensor data is used in theassessment of an object or to monitor performance in differentoperational modes and environmental factors. Sensors can trigger anaction such as turning off the system or modifying operation of thesystem in response to the measured parameter.

In general, cost typically increases with the measurement precision ofthe sensor. Cost can limit the use of highly accurate sensors in pricesensitive applications. Furthermore, there is substantial need forsensors that have low power usage for systems that are battery operated.Ideally, the sensing technology used in a temporarily poweredapplication will not significantly reduce the operating time of thedevice. Moreover, a high percentage of battery-operated devices areportable devices comprising a small volume and low weight. Deviceportability can place further size and weight constraints on the sensortechnology used. Thus, form factor, power dissipation, cost, andmeasurement accuracy are important criteria that are evaluated whenselecting a sensor or measurement system for a specific application.

BRIEF DESCRIPTION OF DRAWINGS

Various features of the system are set forth with particularity in theappended claims. The embodiments herein, can be understood by referenceto the following description, taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic diagram of a dual mode closed loop measurementsystem in accordance with one embodiment;

FIG. 2 is an exemplary flow chart of a method for dual mode closed loopmeasurement in accordance with one embodiment;

FIG. 3 is an exemplary illustration for screw sensor construction viaflex rolling or die stacking in accordance with one embodiment;

FIG. 4 is an exemplary illustration of screw sensor construction viaflex rolling or die stacking insertion in accordance with oneembodiment;

FIG. 5 is an illustrative embodiment of the screw sensor as used in thedual mode closed loop measurement system in accordance with oneembodiment;

FIG. 6 is an illustrative embodiment of the screw sensor as used in thedual mode closed loop measurement system in accordance with oneembodiment;

FIG. 7 is an exemplary illustration of a medical sensing system with thescrew sensor operating in accordance the dual mode closed loop sensingin accordance with one embodiment;

FIG. 8 is an exemplary illustration of a medical sensing systemoperating in accordance the dual mode closed loop sensing in accordancewith one embodiment;

FIG. 9 is a perspective view of the medical sensing device in accordancewith one embodiment;

FIG. 10 is a block model diagram of the sensing module in accordancewith one embodiment;

FIG. 11 is a more detailed block model diagram of the sensing module inaccordance with one embodiment;

FIG. 12 is an exemplary block diagram schematic of a compact low-powerenergy source integrated into an exemplary electronic assembly of themedical sensing device in accordance with one embodiment;

FIG. 13 is an exemplary flow chart of steps performed by the compactlow-power energy source for recharging and operation of the medicalsensing device in accordance with one embodiment;

FIG. 14 is an exemplary block diagram of a propagation tuned oscillator(PTO) in accordance with one embodiment; and

FIG. 15 is another exemplary block diagram of a dual mode closed loopmeasurement system in accordance with one embodiment.

DETAILED DESCRIPTION

Embodiments of the invention are broadly directed to wirelesstransmission coupling between a first device and a second devicetogether forming a measurement system to measure one or more propertiesof a material between the first device and the second device.

The following description of exemplary embodiment(s) is merelyillustrative in nature and is in no way intended to limit the invention,its application, or uses.

Processes, techniques, apparatus, and materials as known by one ofordinary skill in the art may not be discussed in detail but areintended to be part of the enabling description where appropriate. Forexample specific computer code may not be listed for achieving each ofthe steps discussed, however one of ordinary skill would be able,without undo experimentation, to write such code given the enablingdisclosure herein. Such code is intended to fall within the scope of atleast one exemplary embodiment.

Additionally, the sizes of structures used in exemplary embodiments arenot limited by any discussion herein (e.g., the sizes of structures canbe macro (centimeter, meter, and larger sizes), micro (micrometer), andnanometer size and smaller).

Notice that similar reference numerals and letters refer to similaritems in the following figures, and thus once an item is defined in onefigure, it may not be discussed or further defined in the followingfigures.

In one embodiment, a dual-mode closed loop measurement system evaluatesa transit time of energy waves or pulses between two wireless modules.The measurement system can be integrated into medical devices tofacilitate the measurement of physical or physiologic parameters withinor affecting the interface between one or more of the medical devicesand surrounding, but not limited to, tissue, bones, cartilage, fluids,or combinations thereof. Wireless modules may also be integrated intoone or more of the medical devices to facilitate the measurement ofphysical or physiologic parameters of interest external to the medicaldevices having proximity, contacting, or sensing surfaces

In this embodiment, one of the wireless modules functions as a master,actively providing power and control, and the other wireless modulefunctions as a slave, passively receiving power and responding to themaster. The first wireless module operating as the master can include apropagation tuned oscillator, digital logic, counters, and a phasedetector for providing closed loop feedback. The first wireless moduleand second wireless module can operate over a same transmission typeover both legs of the wireless transmission coupling, such aspiezo-to-piezo, or over a mixed transmission type, for example,piezo-to-piezo and inductor-to-inductor. Operating inductor-to-inductoron one leg of the wireless transmission coupling path provides thebenefit of improved energy efficiency. In the later case, dual modeclosed loop operation is established by inductive coupling on a firstleg of the wireless transmission coupling path and energy wavepropagation on a second leg of the wireless transmission coupling path.

In this configuration, an inductor drive circuit on the first deviceactively initiates by way of a transmit inductor a query via inductivecoupling to a receive inductor on the second device via the first leg(or path), the receive inductor in response to the query triggers apiezo component also on the second device to actively emit an energywave that is propagated back to the first device through the propagationmedium to be measured. The second device responsive to receiving theenergy wave monitors the received energy wave for assessing the one ormore properties of the propagation medium, whilst generating a pulsesequence that is fed back to the inductor drive circuit to create aclose-loop feedback path. In this arrangement, the first device and thesecond device operate together via inductive coupling and energy wavepropagation to form the dual-mode closed loop measurement system.

In another embodiment, the dual-mode closed loop measurement systemconstitutes in part a medical diagnostic system for assessing clinicalimplant parameters, for example, bone re-growth integrity, cartilage,fluids, tissue, bond strength, glue joint integrity, and generalbiological integrity with respect to one or more implanted prostheticcomponents, for example, orthopedic knee joint, hip or shoulderimplants. In general, the first and second devices are each placed in ahousing that can be placed in proximity, attached to, or inserted in themuscular-skeletal system. In this embodiment, the first device can beinserted in a bone screw, for example, by flex rolling of the electricalcomponents on a flexible interconnect and insertion in a hollow portionof the screw, or by die stacking of the electrical components in thehollow portion of the bone screw. The second device in this arrangementis a passive component that in one embodiment is a slave to the firstdevice or module.

The bone screw can then be implanted in the bone that is to be assessed,and then functions as the passive aspect of the dual mode closed-loopmeasurement system. A medical reader placed in close proximity to thebone screw and comprising the inductor drive circuit, functions as theactive aspect of the dual mode closed-loop measurement system. The firstdevice in this arrangement is an active component, for example, a masterthat provides the power and control. The medical reader can itself be aninternally placed medical implant device, such as a trial insert, or anexternally engaged medical device, such as a wireless energy sourceconfigured to supply power and also read (receive or process) thepropagated energy waves. The bone screw embodiment is for illustrationonly and is not indicative of limitations on the range of embodimentsfor this or any other application.

In yet another embodiment, the sequence is reversed; that is, the firstdevice actively transmits an energy wave through the propagation mediumto be measured and that is received by the transducer on the seconddevice. The transducer on the second device activates an operativelycoupled inductor, which then generates a low-level electromagneticfield. This field is then in turn measured by a receive inductor on thefirst device. As one example, the field can be externally measured by anRFID reader or an external wireless energy source.

These embodiments illustrate the flexibility the present inventionfacilitates, especially, but not limited to, highly compact embodimentsin a wide range of form factors. This flexibility, over a wide range ofsizes and form factors, may be achieved without compromising measurementaccuracy or resolution. In this example embodiment, the wireless modulesare integrated into screw shaped medical devices to facilitatemeasurement of physical or physiologic parameters of interest. Themedical devices are positioned with the contacting or sensing surfacesengaged with members of the body such that the parameter or parametersof interest affect propagation of energy waves or pulses between themedical devices.

FIG. 1 is a schematic diagram of a dual-mode closed loop measurementsystem 100 in accordance with one embodiment. System 100 comprises afirst circuit A and a second circuit B. Briefly, the dual-mode closedloop measurement system 100 operates via inductive-to-inductive couplingon a first transmission coupling path and piezo-to-piezo on a secondtransmission coupling path. Refer ahead to FIG. 15 to review dual-modeclosed loop measurement operation on a same type of transmissioncoupling (e.g., piezo-to-piezo).

With regard to FIG. 1, the first circuit A comprises a filter 110, adriver circuit 102, an inductor 104, a transducer 106, and a buffercircuit 108. Filter 110 has an input connected to node 124 and anoutput. Filter 110 can be a passive or active filter. In the exampleshown, filter 110 is a passive low pass filter. Driver circuit 102 hasan input connected to the output of filter 110 and a differential outputfor driving a first and second leads of inductor 104. In at least oneexemplary embodiment, inductor 104 is used for powering the system asdisclosed ahead and used as a functional element of the dual-mode closedloop measurement system 100. Using inductor 104 for more than onepurpose lowers cost, reduces the number of components required in thesystem, and minimizes the system footprint. Transducer 106 has a firstlead and a second lead connected to ground. In at least one exemplaryembodiment, transducer 106 is a piezo-electric transducer that operatesin the ultrasonic frequency range. Buffer circuit 108 has a first inputconnected to the first lead of transducer 106, a second lead connectedto ground, and an output connected to node 124. Other circuitry will beexplained ahead for controlling system operations andtransmitting/receiving information.

The second circuit B is a remote device 112 that comprises an inductor114 and a transducer 116. In at least one exemplary embodiment,transducer 116 is a piezo-electric device that operates at ultrasonicfrequencies. Remote sensor 112 is housed separately from the firstcircuit. In at least one exemplary embodiment, the first and secondcircuits can be placed in an organism either temporarily or permanently.In one embodiment, a material 122 to be monitored is bone of a human oranimal, or other biological tissue or engineered material. In anon-limiting example, the first and second circuits A and B are placedin such a manner that living bone is between the circuits. This has thesubstantial benefit of direct monitoring of the bone, which is moreaccurate than monitoring from outside the body. Treatments can bemonitored over time to determine effectiveness. Conditions such asosteolysis can be monitored to determine the rate of change in bonedensity thereby becoming aware of dangerous conditions that can be lifethreatening. Material 122 can be biological or non-biological. Forexample, dual-mode closed loop measurement system 100 can be used tomonitor a glue joint in joint implant. A common failure mechanism of animplanted joint is a reduction in bond strength over time. Cracking ofthe glue and seepage of fluid into the cracks accelerates degradation ofthe bond. The status of the glue joint can be monitored by placing thefirst and second circuits on either side of the glue joint therebyidentifying a weakening glue joint prior to failure and allowing simplercounter measures to be taken to eliminate the issue.

FIG. 2 is an exemplary flow chart 200 of method steps performed bydual-mode closed loop measurement system 100 for assessing materialproperties between the first and second circuits of the medical sensorin accordance with one embodiment. The first and second circuits form aclosed loop system having a first and second path. The first pathcomprises inductors 104 and 114. Inductors 104 and 114 are apredetermined distance 118 from one another (or can be determined) andare electromagnetically connected, for example, analogous to atransformer. Predetermined distance 118 is determined to ensure couplingof inductors 104 and 114 while allowing changes in material 122 to bedetected. In at least one exemplary embodiment, the electromagneticfield couples through material 122. A signal coupled to node 124 orprovided by buffer 108 is filtered by low pass filter 110. The filteredsignal is then provided to driver circuit 102, which drives inductor104. The signal applied to inductor 4 is electromagnetically coupled toinductor 114 in a step 202.

Inductor 114 is connected to transducer 116. The signal coupled toinductor 114 is applied to transducer 116, which activates as shown instep 204. A threshold level of electrical energy can be established tostimulate the piezoelectric transducer. Transducer 116 then emits acorresponding ultrasonic signal into material 122 in a step 206.Transducer 116 is connected to material 122 to ensure transfer of theultrasonic signal. Once transferred the ultrasonic signal propagatesthrough material 122. The ultrasonic signal propagates the predetermineddistance 120 to be received by transducer 106. In at least one exemplaryembodiment, predetermined distance 120 is a known and fixed distance.Alternatively, a sensing system can be used to periodically measure thedistance between transducers 106 and 116.

Transducer 106 receives the ultrasonic signal from material 122 asdisclosed in step 208. In at least one exemplary embodiment, transducer106 is a piezo-electric device that converts the ultrasonic signal to anelectrical signal. Transducer 106 emits a signal that corresponds to thesignal received from material 122 in a step 210. The energy loss throughthe closed loop comprising inductor 104, inductor 114, transducer 116,the material 122 (e.g. propagation-medium), and transducer 106 loop issuch that a signal propagation through the material 122 can be sustainedthereby allowing reliable measurements to be taken within theconstraints of the energy storage capacity of the master/sensing module(e.g., circuits A and B). The signal from transducer 106 is received bybuffer 108. Buffer 108 precisely detects a signal from transducer 106corresponding to an energy wave propagating through the medium. Buffer108 further generates a signal corresponding to the energy wave. In oneembodiment, buffer 108 is a comparator outputting a square wave signal.

The signal from buffer 108 is filtered by low pass filter 110, forexample, by filtering, as shown in step 212. Low pass filter 110 removeshigh frequency components of the square wave signal. The filtered signalfrom buffer 108 is provided back to node 124 thereby closing the signalloop. At step 214, the filtered signal is coupled to the first coil suchthat a closed loop system is formed and that by frequency and timeanalysis identifies changes in the material. The signal through theclosed loop will stabilize over time. The frequency of the signalcorrelates to the properties of material 122. In at least one exemplaryembodiment, with material 122 as bone, the frequency will correspond tobone density. Changes in bone density will modify the transit time ofthe signal across predetermined distance 120, which is a function of thepredetermined distance 120. A direct distance measurement enhances theaccuracy of the results. Closing the loop provides a stable signal thatcan be monitored. The system can be placed in the organism for anextended period of time where it is only powered when a measurement isdesired. This also has the benefits of taking measurements periodicallyover an extended period of time, and offers flexibility to downsize thepassive module even further.

Although components of FIG. 1 were disclosed for enabling aspects of themethod, other embodiments are herein contemplated, for example, a singlemaster/sensing module that queries two or more passive modules,incorporating aspects of Radio Frequency Identification (RFID). In thisconfiguration, a single implanted active can multiplex (mux) multiplevery small passive modules the same way individual sensing assemblagesare multiplexed within the existing sensing module, as will be explainedahead. This may permit applications for 360-degree-like viewing. As willalso be explained ahead, a propagation tuned oscillator operating incontinuous mode, pulse loop, or pulse echo mode is extended foroperation as a dual-mode closed-loop measurement system.

FIG. 3 is an exemplary illustration for screw sensor construction viaflex rolling or die stacking in accordance with one embodiment. One ormore electrical components 332 correspond to the second circuit B ofFIG. 1. Electrical components 332 can be integrated circuits, ASICs, orpassive components. The electrical components are 332 can be affixed toand electrically coupled in a circuit configuration on substrate 331. Ina non-limiting example, substrate 331 can be a flex-cable, ribbon,flexible printed circuit board, or other medium that can be placed in acompact form and provides electrical interconnect for electricalcomponents. The substrate 331 can be altered from a planar shape toachieve a small form factor. For example, substrate 331 can be folded orrolled up to achieve a form factor 333. In one embodiment, inductor 114and transducer 116 is formed on or mounted to substrate 331 and coupledas shown in FIG. 1 as a passive circuit.

FIG. 4 is an exemplary illustration of a screw sensor 335 constructionvia flex rolling or die stacking insertion in accordance with oneembodiment. Screw sensor 335 includes a cavity 337 for receivingsubstrate 331. The substrate 331 in the small form factor 333 isinserted in the cavity 337 of the orthopedic screw in the directionshown. Referring back to FIG. 3, an alternate embodiment stacks theelectrical components 334 of the second circuit B of FIG. 1. The stackeddie in small form factor 333 is similarly inserted in a hollow or cavityof the orthopedic screw 335 shown in FIG. 4. A combination of these twoapproaches can also be performed to construct the orthopedic screw 335.

The sharpness of the bends in the flex substrate 331 can be assessedin-situ to ensure that they do not compromise the integrity of theelectrical traces or interconnect. In one embodiment, the substrate isbetween the interconnect and the walls of the cavity. The stacked dieapproach provides the benefit of minimizing the Z-dimension. The stackheight can be controlled to ensure the proper form factor 333 for acorresponding housing. The stacked die approach can also minimize thefootprint to the largest single package of die and chip-style discretecomponents as well as the complexity of the flex substrate by optimizingthe number of packages versus their individual footprints that must beattached to the flex.

A screw gun is a common tool used by orthopedic surgeons. Similarly,screws are commonly used in orthopedic surgeries to fasten elementstogether. Surgeons will have such familiarity with orthopedic screw 335that an adoption cycle to using the passive circuit coupled therein willbe rapid. Screw 335 is made of bio-compatible materials that can remainin the human body indefinitely. Moreover, screw 335 can be directed veryaccurately in to a predetermined position.

FIG. 5 is an illustrative embodiment of a sensor 306 as used in the dualmode closed loop measurement system in accordance with one embodiment.The measurement system comprises an active sensor 302 and a passivesensor 306. Active sensor 302 and passive sensor 306 respectivelycorrespond to the first circuit A and the second circuit B of FIG. 1.Passive sensor 306 corresponds to screw sensor 335 described in FIG. 4.Sensor 302 can have components similar to that of a sensing moduledisclosed hereinbelow in FIG. 10.

In a non-limiting example sensor 302 is coupled to a surface 308corresponding to a first location of a medium. A transducer of sensor302 is coupled to surface 308. In an example of measuring bone density,the medium is bone 304. Similarly, screw 306 is screwed into a secondlocation of the medium such as bone 304. A transducer of sensor 306couples through the body of the screw to the second location. Sensor 302and sensor 306 form a close-loop that respectively comprises a firstmodule and a second module in communication with each other. Thecommunication between the first and second modules includes a first pathand a second path. As disclosed herein the first and second path can usea same signal type. Alternatively, the first and second paths can havedifferent signal types. In one embodiment, the first path comprises anelectromagnetic or inductive coupling between inductors of sensor 302and sensor 306. A second path comprises an acoustic path from the firstlocation to the second location of bone 304. The second path is coupledby an energy wave propagating between the first and second location ofbone 304. In one embodiment, the energy wave is an ultrasonic energywave or pulse. Sensor 306 is a passive circuit. The transducer of sensor306 is energized by electromagnetic energy received by the inductor ofsensor 306 from the inductor of sensor 302.

Operation of the parameter measurement system is disclosed below. Thefirst module or sensor 302 sends an electromagnetic signal to the secondmodule or sensor 306. The inductors of the first and second modules canbe inductively coupled together similar to a transformer for efficienttransfer of the signal. Sensor 302 is a passive circuit and theelectromagnetic signal received by the inductor of sensor 306 powers thetransducer of sensor 306 to emit one or more energy waves at the secondlocation into bone 304. In the example, sensor 306 is screwed into bone304. The screw to bone interface is a good conductor of an energy wave.The emission of the energy wave can be directional or non-directionalfrom sensor 306. In general, the one or more energy waves propagatetowards the interface 308. The one or more energy waves propagate tointerface 308 where they are detected by sensor 302. Sensor 302 measuresat least one of transit time, frequency, or phase corresponding to thepropagation of an energy wave across a predetermined distance from thefirst location to the second location of bone 304. Closing the loopcomprising the first path and the second path forms a propagation tunedoscillator (PTO). The propagation tuned oscillator and more particularlysensor 302, upon detecting a propagated energy wave at the firstlocation generates an electromagnetic signal that couples from theinductor of sensor 302 to the inductor of sensor 306 thereby initiatingthe emission of a new energy wave. The positive closed-loop feedback ofthe parameter measurement system sustains the emission, propagation,detection, and measurement of the propagated energy waves. The transittime, frequency, or phase of the measured propagated energy waves can berelated to material properties of the propagating medium. In theexample, the transit time, frequency, or phase of an energy wavepropagating through bone has a known relationship to bone density whichis then calculated from the measurements.

FIG. 6 is an illustrative embodiment of the screw sensor 306 as used inthe dual mode closed loop measurement system in accordance with oneembodiment. In this example, the energy wave propagation path differsfrom the path that is perpendicular to the insert direction as shown inFIG. 5 but operates similarly to that described above. The sensor 306 isinserted by rotation inside bone 304. The active sensor 302 is coupledto a bone interface above a head of sensor 306. The propagation path ofan energy wave for detection is aligned in a direction of the insertionpath of sensor 306. In one embodiment, energy waves are emitted fromsensor 306 and propagate a distance 310 through bone 304 to activesensor 302. Thus, sensor 306 can be used to propagate energy waves inmore than one direction or energy waves can be received at multiplelocation points on the bone to measure transit times for differentpaths.

FIG. 7 is an exemplary illustration of a medical sensing system with thescrew sensor 335 operating in accordance the dual mode closed loopsensing in accordance with one embodiment. Screw sensor 335 illustratesa medical sensing system operating in accordance the dual mode closedloop sensing. As shown, the dual mode closed loop sensing system andmore specifically the second circuit B in this embodiment comprises thebone screw 335. The bone screw 335 includes inductor 114 and 116 on aflexible interconnect coupled together as shown in FIG. 1. The sensingdevice 700 serves as the active device (e.g., master) providing power tothe electronic components and operative control. The bone screw 335 withthe embedded electronic components serves as the passive device 712(e.g., slave). Although the illustration shows the top of the bone screwas protruding, this is for illustration and it may be completelyembedded in the bone. In one embodiment, an inductor and coil of thefirst circuit A of FIG. 1 is located in a region 302. The inductor andcoil of the first circuit A and the bone screw 335 bounds a bone region304 such that the devices are spaced a distance 310 apart from oneanother. The bone screw 335 is inserted in a region 306 into the boneusing common orthopedic surgical techniques. The threads of screw 335engage with the bone and firmly hold the device in place eithertemporarily or permanently. In the example, the system measures andmonitors changes to bone density. Between the sensing device 700 and thebone screw 335 is the bone region 734 that is measured by the system,for example, to determine bone density. As will be explained ahead infurther detail, the medical sensing system measures the characteristicsof the energy waves propagating through the bone region 734, namely,transit time and associated parameters of frequency, amplitude and phaseto determine the parameters of interest. This data can be conveyed to areceiver station 710 via wireless for processing and display.

In one embodiment, the medical sensing system comprises an active systemwith transmit/receive sensing, the material to be measured, and apassive component with receive/transmit sensing. The material to bemeasured is between the active system and the passive component. Asshown, the material is perpendicular to the insertion path of thepassive component but can other orientations. The passive components arehoused in a screw common for orthopedic use. The material spacingbetween the active system and the passive component is of a known orpredetermined distance. The transmit path is through electromagneticcoupling from inductor to inductor. The electromagnetic field couplesthrough or around the material. The receive path is acoustic ultrasonicenergy waves coupling piezo-electric transducer to piezo-electrictransducer. A benefit of dual mode sensing is that the transmit inductorto inductor coupling is very energy efficient enabling low powerapplications or temporary powering of the system to take measurements.The material properties, for example bone density, is determined byanalyzing the signal transferred or propagated through the material anddifferential measurements of how the signal changes over time.

FIG. 8 is an exemplary illustration of a medical sensing systemoperating in accordance the dual mode closed loop sensing in accordancewith one embodiment. An external wireless energy source 825 can beplaced in proximity to the sensing device 700 to provide wireless powerto recharge a power source that enables operation. As an example, theexternal wireless energy source 825 generates energy transmissions thatare wirelessly directed to the medical sensing device 700 and receivedas energy waves via resonant inductive coupling. The external wirelessenergy source 825 can modulate a power signal generating the energytransmissions to convey down-link data, which is then demodulated fromthe energy waves at the medical sensing device 700. As one example, themedical sensing device 700 is a load sensor insert device 700 suitablefor use in knee joint replacement surgery. It can intra-operativelyassess a load on the prosthetic knee components (implant) and collectload data for real-time viewing of the load, for example, over variousapplied loads and angles of flexion. The external wireless energy source825 can be used to power the load sensor insert device 700 during thesurgical procedure or thereafter when the surgery is complete and theload sensor insert device 700 is implanted for long-term use.

In a second example, sensing device 700 measures material properties andchanges in material properties over time. The material to be monitoredis placed between sensing device 700 and a component 712, for example,part of a bone screw in accordance with embodiments herein. As shown,the sensor of sensing device 700 is coupled to the tibia. Component 712is inserted in the bone of the tibia in proximity to the sensor ofsensing device 700. Bone material of the tibia is between sensing device700 and component 712. Component 712 includes circuitry that is incommunication with sensing device 700. In at least one exemplaryembodiment, component 712 is formed as a screw that can be inserted intothe tibia at a predetermined location. A screw is a common componentused in orthopedic surgery and will require little training to use. Theclosed loop system comprises sensing device 700, a portion of the tibia(material being sensed), and component 712.

In one system embodiment, the load sensor insert device 700 transmitsmeasured load data to a receiver 710 via one-way data communication overthe up-link channel for permitting visualization of the level anddistribution of load at various points on the prosthetic components.This, combined with cyclic redundancy check error checking, provideshigh security and protection against any form of unauthorized oraccidental interference with a minimum of added circuitry andcomponents. This can aid the surgeon in making any adjustments needed toachieve optimal joint balancing. In addition to transmitting one-waydata, communications can occur over the up-link channel to the receiverstation 710. The load sensor insert device 700 can receive down-linkdata from the external wireless energy source 825 during the wirelesspower recharging operation. The down-link data can include componentinformation, such as a serial number, or control information, forcontrolling operation of the load sensor insert device 700. This datacan then be uploaded to the receiving system 710 upon request via theone-way up-link channel, in effect providing two-way data communicationsover separate channels.

As shown, the wireless energy source 127 can include a power supply 826,a modulation circuit 827, and a data input 828. The power supply 826 canbe a battery, a charging device, a power connection, or other energysource for generating wireless power signals to charge the load sensorinsert device 700. The external wireless energy source can transmitenergy in the form of, but not limited to, electromagnetic induction, orother electromagnetic or ultrasound emissions. The data input 828 can bea user interface component (e.g., keyboard, keypad, touchscreen) thatreceives input information (e.g., serial number, control codes) to bedownloaded to the load sensor insert device 700. The data input 828 canalso be an interface or port to receive the input information fromanother data source, such as from a computer via a wired or wirelessconnection (e.g., USB, IEEE802.16, etc.). The modulation circuitry 827can modulate the input information onto the power signals generated bythe power supply 826.

During a knee procedure, the surgeon can affix a femoral prostheticcomponent 704 to the femur 702 and a tibial prosthetic component 806 tothe patient's tibia 708. The tibial prosthetic component 706 can be atray or plate affixed to a planarized proximal end of the tibia 708. Thesensing device 700 is a load sensing insert that is fitted between theplate of the tibial prosthetic component 706 and the femoral prostheticcomponent 704. These three prosthetic components (704, 700 and 806)enable the prostheses to emulate the functioning of a natural kneejoint.

The sensing device 700 can be a mechanical replica of a final tibialimplant. It can measure loads at various points (or locations) on thefemoral prosthetic component 704 and transmit the measured data to areceiving station 710 by way of a loop antenna. The receiving station710 can include data processing, storage, or display, or combinationthereof and provide real time graphical representation of the level anddistribution of the load.

As one example, the sensing device 700 can measure forces (Fx, Fy, Fz)with corresponding locations on the femoral prosthetic component 704 andthe tibial prosthetic component 806. It can then transmit this data tothe receiving station 710 to provide real-time visualization forassisting the surgeon in identifying any adjustments needed to achieveoptimal joint balancing.

In the second example, a closed loop signal has a path through a portionof the bone of the tibia. The closed loop signal will correlate tomaterial properties such as bone density. Thus, changes in bone densitycan be monitored and preventative actions taken when the conditionswarrant concern. Furthermore, monitoring can provide valuableinformation on how effective the treatments are. The system can betemporary or permanent.

FIG. 9 is a perspective view of the medical sensing device 700 inaccordance with one embodiment. As illustrated, the sensing device 700can include a sensing module 900 and an insert 702. The sensing module700 can securely fit within the insert dock 702. The insert dock 702 cansecurely attach or slide onto the tibial prosthetic component 806 ofFIG. 8. The prosthetic components of FIG. 8 can be manually coupledprior to surgical placement or during the surgery. The sensing module700 in other embodiments (without the insert dock 702) can affixdirectly to load bearing surfaces exposed to forces, for example, forcesapplied upon a load bearing component during flexion of the joint.Although illustrated as separate, in yet another embodiment, the sensingmodule 700 and insert dock 702 can be combined together as an integratedsensing module.

The sensing module 700 is an encapsulating enclosure with a unitary mainbody and load bearing contact surfaces that can be, but are not limitedto, dissimilar materials, combined to form a hermetic module or device.The components of the encapsulating enclosure may also consist of, butare not limited to, bio-compatible materials. For medical applications,the encapsulating enclosure may be required to be hermetic. Theencapsulating enclosure can comprise biocompatible materials, forexample, but not limited to, polycarbonate, steel, silicon, neoprene,and similar materials.

The range of nonmedical and medical applications for the sensing deviceis extensive. Requirements of individual applications of wirelessmodules or devices drive the selection of the power source andarchitecture, the form of energy and transducers coupled to the mediumof propagation, as well as the form of energy and transducers forinter-module or inter-device communication. One factor driving theselection of the forms of energy and energy transducers is the mode ofmeasurement operation that fits each application and parameter orparameters of interest within the body or physical system being studied.The modes of measurement may include, but are not limited to,short-term, temporary measurement, point-in-time measurement, andcontinuous measurement. Up to four separate forms or frequencies ofenergy may be used by pairs of wireless modules or devices duringcharging, measuring, and communication operations. These include energyfor powering each wireless module or device, energy waves or pulsescoupled through the propagating medium within the body or physicalsystem, energy pulses for inter-module wireless module or devicecommunication, and energy waves for telemetry communication ofmeasurement data to external instruments or equipment. For example, butnot limited to, electromagnetic induction that is used for charging theenergy storage device within each wireless module or device, ultrasonicwaves or pulses may be propagated through the propagation medium, lowfrequency RF pulses may be used for inter-module or inter-devicecommunication enabling closed-loop measurement, and higher frequency RFemissions may be used for telemetry to communicate measurement data toexternal instruments or devices. Obviously, there are many otherpossible combinations and permutations, including, but not limited to,the use of optical transducers or lasers and light or infrared energywaves or pulses. For modes of measurement that charge the internal powersupply before beginning measurement operation only three distinct formsor frequencies of energy may be required during measurement and datareporting operations.

FIG. 10 is a block model diagram of the sensing module 900 in accordancewith one embodiment. It should be noted that the sensing module 900 cancomprise more or less than the number of components shown. Asillustrated, the sensing module 900 includes one or more sensingassemblages 1003, a transceiver 1020, an energy storage 1030, electroniccircuitry 1007, one or more mechanical supports 1015 (e.g., springs),and an accelerometer 1002.

The sensing assemblage 1003 can be positioned, engaged, attached, oraffixed to the load bearing contact surfaces 1006. Mechanical supports1015 serve to provide proper balancing of load bearing contact surfaces1006. Load bearing surfaces 1006 can move and tilt with changes inapplied load; actions which can be transferred to the sensingassemblages 1003 and measured by the electronic circuitry 1007. Theelectronic circuitry 1007 measures physical changes in the sensingassemblage 1003 to determine parameters of interest; for example, alevel, distribution and direction of forces acting on the load bearingcontact surfaces 1006. Power for the sensing module 900 is provided bythe energy storage 1030.

As one example, the sensing assemblage 1003 can comprise an elastic orcompressible propagation structure 1005 between a first transducer 1004and a second transducer 1014. In the current example, the transducerscan be an ultrasound (or ultrasonic) resonator, and the elastic orcompressible propagation structure 1005 can be an ultrasound (orultrasonic) waveguide (or waveguides). The electronic circuitry 1007 iselectrically coupled to the sensing assemblages 1003 and translateschanges in the length (or compression or extension) of the sensingassemblages 1003 to parameters of interest, such as force. It measures achange in the length of the propagation structure 1005 (e.g., waveguide)responsive to an applied force and converts this change into electricalsignals which can be transmitted via the transceiver 1020 to convey alevel and a direction of the applied force. In other arrangements hereincontemplated, the sensing assemblage 1003 may require only a singletransducer. In yet other arrangements, the sensing assemblage 1003 caninclude piezoelectric, capacitive, optical or temperature sensors ortransducers to measure the compression or displacement. It is notlimited to ultrasonic transducers and waveguides.

The accelerometer 1002 can measure acceleration and static gravitationalpull. It can include single-axis and multi-axis structures to detectmagnitude and direction of the acceleration as a vector quantity, andcan be used to sense orientation, vibration, impact and shock. Theelectronic circuitry 1007 in conjunction with the accelerometer 1002 andsensing assemblies 1003 can measure parameters of interest (e.g.,distributions of load, force, pressure, displacement, movement,rotation, torque and acceleration) relative to orientations of thesensing module 900 with respect to a reference point. In such anarrangement, spatial distributions of the measured parameters relativeto a chosen frame of reference can be computed and presented forreal-time display.

The transceiver 1020 can include a transmitter 1009 and an antenna 1010to permit wireless operation and telemetry functions. In variousembodiments, the antenna 1010 can be configured by design as anintegrated loop antenna. The integrated loop antenna can be configuredat various layers and locations on the electronic substrate withelectrical components and by way of electronic control circuitry toconduct efficiently at low power levels. Once initiated the transceiver1020 can broadcast the parameters of interest in real-time. Thetelemetry data can be received and decoded with various receivers, orwith a custom receiver. The wireless operation can eliminate distortionof, or limitations on, measurements caused by the potential for physicalinterference by, or limitations imposed by, wiring and cables connectingthe sensing module 900 with a power source or control circuitry or withassociated data collection, storage, or display equipment.

The transceiver 1020 receives power from the energy storage 1030 and canoperate at low-power over various radio frequencies by way of efficientpower management schemes, for example, incorporated within theelectronic circuitry 1007. As one example, the transceiver 1020 cantransmit data at selected frequencies in a chosen mode of emission byway of the antenna 1010. The selected frequencies can include, but arenot limited to, ISM bands recognized in International TelecommunicationUnion regions 1, 2 and 3. A chosen mode of emission can be, but is notlimited to, Gaussian Frequency Shift Keying, (GFSK), Amplitude ShiftKeying (ASK), Phase Shift Keying (PSK), Minimum Shift Keying (MSK),Frequency Modulation (FM), Amplitude Modulation (AM), or other versionsof frequency or amplitude modulation (e.g., binary, coherent,quadrature, etc.).

Briefly, antenna 1010 can be integrated with components of the sensingmodule 900 to provide the radio frequency transmission. The substratefor the antenna 1010 and electrical connections with the electroniccircuitry 1007 can further include a matching network. This level ofintegration of the antenna and electronics enables reductions in thesize and cost of wireless equipment. Potential applications may include,but are not limited to any type of short-range handheld, wearable, orother portable communication equipment where compact antennas arecommonly used. This includes disposable modules or devices as well asreusable modules or devices and modules or devices for long-term use.

Minimizing circuitry or antenna for downlink telemetry can enable theconstruction of, but not limited to, highly compact wireless devices fora wide range of non-medical and medical applications. Examples ofpotential medical applications may include, but are not limited to,implantable devices, modules within implantable devices, intra-operativeimplants or modules within intra-operative implants or trial inserts,modules within inserted or ingested devices, modules within wearabledevices, modules within handheld devices, modules within instruments,appliances, equipment, or accessories of all of these, or disposableswithin implants, trial inserts, inserted or ingested devices, wearabledevices, handheld devices, instruments, appliances, equipment, oraccessories to these devices, instruments, appliances, or equipment.

The energy storage 1030 provides power to electronic components of thesensing module 900. It can be charged by wired energy transfer,short-distance wireless energy transfer or a combination thereof.External power sources can include, but are not limited to, a battery orbatteries, an alternating current power supply, a radio frequencyreceiver, an electromagnetic induction coil, a photoelectric cell orcells, a thermocouple or thermocouples, or an ultrasound transducer ortransducers. By way of the energy storage 1030, the sensing module 900can be operated with a single charge until the internal energy isdrained. It can be recharged periodically to enable continuousoperation. For compact electronic modules or devices, ultra-capacitorsor super capacitors, or other form of capacitors provide many benefitsover other rechargeable technologies.

The energy storage 1030 can utilize common power management technologiessuch as replaceable batteries, supply regulation technologies, andcharging system technologies for supplying energy to the components ofthe sensing module 900 to facilitate wireless applications. The energystorage 1030 minimizes additional sources of energy radiation requiredto power the sensing module 900 during measurement operations. In oneembodiment, as illustrated, the energy storage 1030 can include acapacitive energy storage device 1008 and an induction coil 1011.External source of charging power can be coupled wirelessly to thecapacitive energy storage device 1008 through the electromagneticinduction coil or coils 1011 by way of inductive charging. The chargingoperation can be controlled by power management systems designed into,or with, the electronic circuitry 1007. As one example, during operationof electronic circuitry 1007, power can be transferred from capacitiveenergy storage device 1008 by way of efficient step-up and step-downvoltage conversion circuitry. This conserves operating power of circuitblocks at a minimum voltage level to support the required level ofperformance.

As previously noted, in one configuration, the energy store 1030 cancommunicate downlink data to the transceiver 1020 during a rechargingoperation. For instance, downlink control data can be modulated onto theenergy source signal and thereafter demodulated from the induction coil1011 by way of electronic control circuitry 1007. This can serve as amore efficient way for receiving downlink data instead of configuringthe transceiver 1020 for both uplink and downlink operation. As oneexample, downlink data can include updated control parameters that thesensing module 900 uses when making a measurement, such as externalpositional information, or for recalibration purposes, such as springbiasing. It can also be used to download a serial number or otheridentification data.

The electronic circuitry 1007 manages and controls various operations ofthe components of the sensing module 900, such as load sensing, powermanagement, telemetry, and acceleration sensing. It can include analogcircuits, digital circuits, integrated circuits, discrete components, orany combination thereof. In one arrangement, it can be partitioned amongintegrated circuits and discrete components to minimize powerconsumption without compromising performance. Partitioning functionsbetween digital and analog circuit enhances design flexibility andfacilitates minimizing power consumption without sacrificingfunctionality or performance. Accordingly, the electronic circuitry 1007can comprise one or more Application Specific Integrated Circuit (ASIC)chips, for example, specific to a core signal processing algorithm.

In another arrangement, the electronic circuitry can comprise acontroller such as a programmable processor, a Digital Signal Processor(DSP), or a Micro-Controller (μC), with associated storage memory andlogic. The controller can utilize computing technologies with associatedstorage memory such a Flash, ROM, RAM, SRAM, DRAM or other liketechnologies for controlling operations of the aforementioned componentsof the sensing module 900. In one arrangement, the storage memory maystore one or more sets of instructions (e.g., software) embodying anyone or more of the methodologies or functions described herein. Theinstructions may also reside, completely or at least partially, withinother memory, and/or a processor during execution thereof by anotherprocessor or computer system.

FIG. 11 is a more detailed block model diagram of the sensing module 900in accordance with one embodiment. The diagram depicts in one embodimenta block diagram 1100 of the sensing module 900 where certain componentsare replaced or supplemented with specialized ASICs. As illustrated, thecharging circuit 1104 can be an integrated circuit operatively coupledto the inductor coil 1102 for charging the energy store 1106. Inductorcoil 1102 can also be used in a sensing operation as describedhereinabove. The power management circuitry 1108 can manage wired andwireless charging operations for operating the sensing module 1100. Asanother example, electronic circuitry 1007 is supplemented with amatching network, zero-crossing or edge detect receiver, and propagationtuned oscillator to precisely track transit time of ultrasound waves inthe elastic or compressible propagation structures. Integration of thetelemetry transmitter and sensor modules enables construction of a widerange of sizes of the sensing module 1100. This facilitates capturingdata, measuring parameters of interest and digitizing that data, andsubsequently communicating that data to external equipment with minimaldisturbance to the operation of the body, instrument, appliance,vehicle, equipment, or physical system for a wide range of applications.Moreover, the level of accuracy and resolution achieved by the totalintegration of communication components, transducers, waveguides, andoscillators to control the operating frequency of the ultrasoundtransducers enables the compact, self-contained measurement moduleconstruction.

The energy storage 1106 and power management 1108 sections areresponsible for powering components of the sensing module 1100. Thelow-power energy storage 1106 is self-powered using capacitors, ultracapacitors, super capacitors, or other forms of capacitors. Charge canbe applied to the selected energy storage device 1106 throughelectromagnetic induction, radio frequency induction, photocells,thermocouples, ultrasound transducers, or temporary connection tobatteries external power supplies. The embedded energy storage 1106minimizes additional sources of energy radiation (to provide power forthe wireless load sensing module or device) within the operating roomduring the implant procedure. Capacitors, ultra capacitors, orsuper-capacitors for energy storage enable high levels ofminiaturization. Wireless charging as well as wirelessly transferringmeasurement data eliminates distortion of measurements caused byphysical interference with movement, instruments, and standard surgicalprocedures during the implant procedure.

Benefits of ultra capacitors, super capacitors, or other form ofcapacitors as a power source instead or, or in conjunction with, otherpower sources or rechargeable technologies include, but are not limitedto, enabling a high level of miniaturization as ultra capacitors orsuper capacitors are smaller than smallest available battery for thesame level of energy and power for many low power applications orapplications that require power only intermittently or as a short-termbackup for other power sources.

For applications that require power only intermittently, ultracapacitors, super capacitors, or other form of capacitors enable rapidrecharge, much faster than battery technologies and rechargeablechemistries, regardless of their energy capacity. A charge time of acapacitively powered system from a completely uncharged state can beachieved in a short period of time (minutes) because no chemicalprocesses are involved in charging capacitors. This may be compared tocharge times on the order of hours for battery technologies thattypically do not charge at a rate faster than one-half the energystorage capacity of the battery within one hour. In practice, manybattery applications charge at a much slower rate. Ultra capacitors,super capacitors, or other form of capacitors have almost indefinitelifetimes. There is no deterioration of a capacitor's storage capacitywhen uncharged, regardless of length of time at zero charge.Overcharging capacitors may pose less risk to electronics within anelectronic module or device than overcharging batteries might pose. Inaddition, ultra capacitors, super capacitors, or other forms ofcapacitors eliminate storage and disposal limitations of batteries withno risk of chemical leakage. Furthermore, ultra capacitors, supercapacitors, or other form of capacitors may be surface-mountable andintegrate well into the electronics assemblies and standardsurface-mount electronic assembly processes.

Use of ultra capacitors, super capacitors, or other form of capacitorsto provide operating power for wireless devices, telemetry devices, ormedical devices provides design, construction, and operating flexibilityover a wide range of potential applications. Ultra-capacitors, ultracapacitors, or super capacitors, or other form of capacitors may becharged by connecting them to other power sources such as, but notlimited to, a battery or batteries, an alternating current (AC) powersupply, a radio frequency (RF) receiver, electromagnetic induction coilor coils, photoelectric cell or cells, thermocouple or thermocouples, oran ultrasound transducer or transducers. For compact electronic modulesor devices, ultra-capacitors, ultra capacitors, or super capacitors, orother form of capacitors provide many benefits over other rechargeabletechnologies.

Applications may include, but are not limited to, disposable modules ordevices as well as reusable modules or devices and modules or devicesfor long term use. In addition to non-medical applications, examples ofa wide range of potential medical applications may include, but are notlimited to, implantable devices, modules within implantable devices,intra-operative implants or modules within intra-operative implants ortrial inserts, modules within inserted or ingested devices, moduleswithin wearable devices, modules within handheld devices, modules withininstruments, appliances, equipment, or accessories of all of these, ordisposables within implants, trial inserts, inserted or ingesteddevices, wearable devices, handheld devices, instruments, appliances,equipment, or accessories to these devices, instruments, appliances, orequipment.

FIG. 12 is an exemplary block diagram schematic of a compact low-powerenergy source 1200 integrated into an exemplary electronic assembly ofthe medical sensing device in accordance with one embodiment. Theschematic illustrates one embodiment of the capacitive energy storage1200 having an induction coupling to an external power source 1202 totransfer energy to a super capacitor as an energy storage deviceoperating power for an electronic module or device. The compactlow-power energy source 1200 can comprise an induction coil 1204, arectifier 1206, a regulator 1208, a capacitive energy storage device1210, a power management circuit 1212, and operating circuitry 1214. Thelatter circuits can be analog or discrete components, assembled in partor whole with other electronic circuitry, custom designed as an ASIC, orany combination thereof.

The external energy source 1202 can be coupled to a battery or batteriesor an alternating current power supply. For example, external energysource 1202 can be an external hand-held device with its own batterythat wirelessly transfers charge from the battery of the hand-helddevice to the energy source 1200 of the sensing device. The surgeon ortechnician can hold the hand-held device in close proximity to thesensing device prior to or during orthopedic surgery to providesufficient charge to operate the device during the procedure. Thesensing device as a long-term implant can be charged by the patient athis or her own convenience to initiate a measurement process thatprovides information on the implant status. In other embodiments, thesensing device being powered by charge from external energy source 1202can communicate a signal to indicate a recharging operation isnecessary, for example, when in the proximity of a charging device.

External energy source 1202 can be coupled wirelessly to capacitiveenergy storage device 1210 through electromagnetic induction coil orcoils 1204, rectifier 1206 and regulator 1208. The charging operation iscontrolled by power management circuitry 1212. During operation ofoperating circuitry 1214, power is transferred from capacitive energystorage device 1210 by power management circuitry 1212 that includes,but is not limited to, efficient step-up and step-down voltage convertercircuitry that conserves operating power of circuit blocks at theminimum voltage levels that support the required level of performance.Clock frequencies are also optimized for performance, power, and size toassure digital circuit blocks operate at the optimum clock rates thatsupport the required level of performance. Circuit components arepartitioned among integrated circuits and discrete components to alsominimize power consumption without compromising performance.Partitioning functions between digital and analog circuit also enhancesdesign flexibility and facilitates minimizing power consumption withoutsacrificing functionality or performance.

FIG. 13 is an exemplary flow chart of steps performed by the compactlow-power energy source 1200 for recharging and operation of the medicalsensing device in accordance with one embodiment. The method 1300 can bepracticed with more or less than the number of steps shown and is notlimited to the order shown. To describe the method 1300, reference willbe made to the components of other figures described hereinabovealthough it is understood that the method 1300 can be implemented in anyother manner using other suitable components. The sensing module 900described in FIG. 9 including capacitive energy storage capability andhighly efficient, low power operating performance can be used toillustrate the operating principles of method 1300. The method 1300 isinitiated when the external power source 1202 begins transmitting powerwithin range of the induction coil or coils 1204 of the sensing module900 in a step 1302. In a step 1304, the induction coils 1204 are coupledto the electromagnetic waves such that the electromagnetic waves aresensed. The induction coil or coils 1204 are energized by the powertransmissions from external power source 1202. In a step 1306, thecoupled electromagnetic waves creates an AC voltage signal in inductioncoil or coils 1204. In a step 1308, the rectifier 1206 rectifies the ACvoltage signal to produce a rectified voltage signal. In one embodiment,the voltage level across induction coil or coils 1204 rises to a levelthat a rectified signal is generated by full-wave rectifier 1206. In astep 1310, the rectified voltage signal is used to charge the capacitiveenergy storage device 1210, which holds the charge. In a non-limitingexample, the energy storage device 1210 is a supercapacitor having asmall form factor having enough storage capability to power the sensingmodule 900 for a predetermined period of time. In steps 1310 and 1312,voltage regulator 1208 ensures that the capacitive energy storage device1210 is charged to, and maintains a voltage level that is greater thanthe required operating voltage of the sensing module 900. Powermanagement circuitry 1212 monitors the level of charge on capacitiveenergy storage device 1210 in step 1312 to determine if the voltageexceeds a threshold. The threshold can correspond to a shunt thresholdestablished by the regulator 1208. The operating electronics circuitry1214 is enabled when it is determined in decision block 1312 that anadequate level of charge has been stored to power the system for atleast the predetermined time period.

In a step 1314, the power management circuitry 1212 disconnects theenergy storage device 1210 from the charging circuitry (1204, 1206, and1208) when the coupling with external power source 1202 is removed orterminated. Power management circuitry 1212 continues to monitor thelevel of charge on capacitive energy storage device 1210. The powermanagement circuitry 1212 powers down the sensing module 900 with theoperational circuitry 1214 when the charge level falls below apredetermined threshold. The power management circuitry 1212subsequently discharges remaining charge on the energy storage device1210 to prevent unreliable, intermittent, or erratic operation of theoperational circuitry 1214.

Under nominal conditions, a charge time from zero charge to fullycharged is approximately 3 minutes. In one embodiment, the maximumcharge time is specified to be no greater than 7 minutes. The chargingtime of a capacitively powered system is a major improvement over thetwo hours or more required to fully charge a battery from zero chargeregardless of battery capacity. The capacitive energy storage device1210 can include capacitors with solid dielectrics to have longerlifetimes than batteries and also when uncharged, regardless of lengthof time at zero charge. In one arrangement, the wireless chargingoperation can be performed by electromagnetic induction before removalof any sterile packaging. The capacitive energy storage device 1210 isapplicable for powering chronic active implantable devices where datacollection is discrete point-of-time measurements rather thancontinuous, fulltime data collection and storage.

FIG. 14 is an exemplary block diagram 1400 of a propagation tunedoscillator (PTO) 1404 in accordance with one embodiment. Diagram 1400illustrates propagation tuned oscillator (PTO) 1404 maintaining positiveclosed-loop feedback of energy waves 1402 in one or more energypropagating structures 1403 of a sensing assemblage 1401. The sensingassemblage 1401 comprises a first transducer 1405, a second transducer1406, and a waveguide 1403 (energy propagating structure). Firsttransducer 1405 is coupled to waveguide 1403 at a first location. Secondtransducer 1406 is coupled to the waveguide 1403 at a second location.The sensing assemblage 1401 is affixed to load bearing or contactingsurfaces 1408. External forces applied to the contacting surfaces 1408compress the waveguide 1403 and change the length of the waveguide 1403.This moves transducers 1405 and 1406 closer to together. The change inlength of waveguide 1403 affects the transmit time 1407 of energy waves1402 propagating between transducers 1405 and 1406. The PTO 1404 inresponse to these physical changes alters the oscillation frequency ofthe energy waves 1402 to achieve resonance. In one embodiment, theenergy waves 1402 are ultrasonic in frequency. The change in oscillationfrequency due to a change in the length of waveguide 1403 isaccomplished by way of the PTO 1404 in conjunction with a pulsegenerator, a mode control, and a phase detector.

Notably, changes in the waveguide 1403 (energy propagating structure orstructures) alter the propagation properties of the medium ofpropagation (e.g. transmit time 1407). Due to the closed-loop operationshown, the PTO 1404 changes the resonant frequency of the oscillator andaccordingly the frequency of oscillation of the closed loop circuit. Inparticular, the PTO 1404 adjusts the oscillation frequency to be aninteger number of waves. The digital counter 1409 in conjunction withelectronic components counts the number of waves to determine thecorresponding change in the length of the waveguide 1403. The change inlength of waveguide 1403 is in direct proportion to the external forcebeing applied to surfaces 1408 thus enabling the conversion of changesin parameter or parameters of interest into electrical signals.

Briefly, the operation of propagation tuned oscillator 1404 is disclosedhereinbelow. Transducer 1405 emits energy waves 1402 into waveguide 1403at the first location. The frequency of ultrasound energy waves 1402emitted by ultrasound resonator or transducer 1405 is controlled bypropagation tuned oscillator 1404. Emitted energy waves propagate fromthe first location of the waveguide 1403 to the second location. Adetecting transducer can be either a separate ultrasound transducer orthe emitting transducer 1405 itself depending on the selected mode ofpropagation. As shown, transducer 1406 is a separate detectingtransducer coupled to the second location of waveguide 1403. The transittime 1407 of ultrasound waves 1402 propagating through the waveguide1403 determines the period of oscillation of propagation tunedoscillator 1404. As previously noted, changes in external forces orconditions applied to surfaces 1408 affect the propagationcharacteristics of waveguide 1403 and alter transit time 1407. Thenumber of wavelengths of ultrasound energy pulses or waves 1402 is heldconstant by propagation tuned oscillator 1404. This constraint forcesthe frequency of oscillation of propagation tuned oscillator 1404 tochange when the length of waveguide 1403 is modified. The resultingchanges in frequency are captured with digital counter 1409 as ameasurement of changes in external forces or conditions applied tosurfaces 1408.

FIG. 15 is another exemplary block diagram 1500 of a dual mode closedloop measurement system in accordance with one embodiment. The diagram1500 illustrates signal paths and interfaces with a propagation tunedoscillator or oscillators that iteratively adjust the repetition rate ofenergy pulses for measurement of the transit time of energy pulsesbetween two wireless modules. Propagation tuned oscillator 1503 drivesthe digital interface coupled to the transducer 1504 to provide energywave or pulse emission into a medium 1505 controlled by wireless moduleor device 1502. The transducer 1504 contacts or is engaged at aninterface 1524 of energy propagating medium 1505.

A measurement process is initiated by the emission of energy pulses orwaves 1506 into the medium 1505. In one embodiment, the energy wavepropagation occurs of within a body or physical system 1501 such as amuscular-skeletal system or components of artificial orthopedic implantsof the muscular-skeletal system. The transit time of energy pulses orwaves propagating through the medium 1505 changes as the energypropagation characteristics of medium 1505 are influenced by changes inthe parameter or parameters of interest.

The energy waves 1506 are detected by a second energy pulse or wavedetecting wireless module or device 1507. Second module 1507 includes atransducer 1508 contacting or engaged with propagating medium 1505 at aninterface 1526. Transducer 1508 is coupled to digital circuitry 1509within wireless module or device 1507 driving a digital interface to aseparate transducer 1510. The transducer 1510 is controlled to emitenergy of a different form than the energy received from the firstwireless module or device 1502. For example, transducer 1508 receives anultrasonic acoustic energy wave or pulse and transducer 1510 emits anelectromagnetic wave. The transducer 1510 emits an energy wave 1511 thatcorresponds to and is in response to the detection of energy wave orpulse 1506. The energy wave or pulse 1511 is detected by transducer 1512on wireless module or device 1502. Transducer 1512 is interfaced topropagation tuned oscillator 1503 thus enabling closed-loop control ofthe stream of energy waves or pulses propagating through medium ofpropagation 1505. The resulting changes in the repetition rate ofoperation can be readily captured with digital counter 1509 oraccumulator to capture data on the parameter or parameters of interest.

The operation of first module 1502 and second module 1507 forpropagating energy waves or pulses through medium 1505 in a positivefeedback closed-loop is disclosed further hereinbelow. A clock 1521provides a pulse A that is coupled to transducer 1504 within the firstwireless module or device 1502. The pulse A triggers one or more energywaves or pulses 1506 to be emitted into the medium 1505 at the interface1524. The energy waves or pulses 1506 propagate in the medium 1505within the body or physical system 1501 under study. The transit time ofenergy waves or pulses 1506 depend on the energy propagationcharacteristics of the propagation medium 1505.

The energy waves or pulses 1506 are detected by the second wirelessmodule or device 1507 when they propagate to the interface 1526. Thesecond wireless module 1507 in response to the received energy wave 1506emits a different form of energy pulse 1511 back to the first wirelessmodule or device 1502. The energy pulse or wave 1511 is detected by thefirst wireless module or device 1502 and converted into a digital pulseB. The digital pulse B is compared with the initial pulse A by the phasedetector 1514 within the propagation tuned oscillator 1503 within thefirst wireless module 1502. The phase detector 1514 in view of the phasedifference drives changes in the repetition rate of the digital clock1521 driving the energy transducer 1504 within the first wireless moduleor device 1502.

The process continues to iterate by way of the PTO 1503 until the phasedifference between the energy waves or pulses emitted into the medium1505 and received by the first wireless module or device 1502 isminimized. The repetition rate of the clock 1521 is measured byaccumulating cycle counts by counter 1509 over a known time base.Changes in the parameter or parameters of interest change thepropagation characteristics of energy waves or pulses 1506 within thepropagation medium 1505 between the two wireless modules or devices 1502and 1507. The propagation tuned oscillator 1503 continually updates therepetition rate of the digital clock 1521 to reduce phase differencesbetween the energy waves or pulses emitted 1506 and received 1511 by thefirst wireless module or device 1502. The accumulated count by counter1509 is transferred to external equipment for additional processing,storage, or display, or combinations of these. The accumulated countwithin counter 1509 is periodically updated to maintain real-time dataon changes in the parameter or parameters of interest.

While the present invention has been described with reference toparticular embodiments, those skilled in the art will recognize thatmany changes may be made thereto without departing from the spirit andscope of the present invention. Each of these embodiments and obviousvariations thereof is contemplated as falling within the spirit andscope of the invention.

What is claimed is:
 1. An orthopedic screw and system comprising: afirst circuit in a module wherein the module is configured to be placedat first location; and a second circuit in a cavity of a screw whereinthe screw is configured to fasten to a muscular-skeletal system at asecond location, wherein the second circuit comprises a passive circuit,wherein the module and screw are configured to form a closed loop torepeatably propagate a signal through the first and second circuit andwherein the signal corresponds to a parameter being measured.
 2. Theorthopedic screw and system of claim 1 where the passive circuit couplesto the screw.
 3. The orthopedic screw and system of claim 2 where thepassive circuit emits an energy wave to the muscular-skeletal systemthrough the screw.
 4. The orthopedic screw and system of claim 1 wherethe first circuit and the second circuit is configured to supportmeasurement of a parameter related to the muscular-skeletal system. 5.The orthopedic screw and system of claim 1 where the second circuitcomprises: an inductor; and a transducer operatively coupled to theinductor.
 6. The orthopedic screw and system of claim 5 furtherincluding a substrate where the inductor and transducer are coupled tothe substrate and where the substrate includes interconnect for couplingthe inductor to the transducer.
 7. The orthopedic screw and system ofclaim 6 where die of the inductor and transducer is stacked.
 8. Theorthopedic screw and system of claim 1 wherein the signal is inductivelycoupled from the module to the screw.
 9. The orthopedic screw and systemof claim 8 wherein the signal received by the module from the screw isacoustic.
 10. The orthopedic screw and system of claim 9 wherein thesignal comprises an electrical signal, an ultrasonic signal, or anelectromagnetic signal in the closed loop.
 11. The orthopedic screw andsystem of claim 10 wherein the transit time, frequency, or phase of thesignal is measured.
 12. An orthopedic screw and system comprising: ascrew including a cavity configured to fasten to a muscular-skeletalsystem; and a circuit in the cavity where the circuit consists of apassive circuit configured to transmit an energy wave to themuscular-skeletal system wherein a transducer and an inductor couple toa substrate, wherein the substrate includes interconnect coupling thetransducer to the inductor, and wherein die of the inductor and thetransducer is stacked.
 13. The orthopedic screw of claim 12 furtherincluding a module configured to be in closed-loop feedback with theinductor and the transducer of the orthopedic screw.
 14. The orthopedicscrew and system of claim 13 wherein the module is configured to be inclosed-loop feedback with the inductor and the transducer of theorthopedic screw.
 15. The orthopedic screw and system of claim 14 wherethe module is configured to be coupled in a first path to the inductorof the orthopedic screw electromagnetically.
 16. The orthopedic screwand system of claim 15 where the module is configured to be coupled in asecond path to the transducer of the orthopedic screw ultrasonically.17. A measurement system comprising: a module having a first circuitwherein the first circuit is a passive circuit; a screw configured tofasten to a muscular-skeletal system wherein the screw includes a secondcircuit, wherein a signal propagates at least two times in a closed loopbetween the module and the screw, and wherein the transit time,frequency, or phase of the signal corresponds to a parameter beingmeasured.
 18. The measurement system of claim 17 where the passivecircuit of the screw comprises an inductor and a transducer.
 19. Themeasurement system of claim 18 where the signal from the module to thescrew is configured to be an electro-magnetic signal coupled to theinductor of the passive circuit of the screw.
 20. The measurement systemof claim 19 where the signal received by the module is configured to bean acoustic signal output by the transducer of the passive circuit ofthe screw.